National Oilwell Varco, the largest U.S. oilfield equipment maker, will buy fiberglass pipe provider Ameron International for $772 million to expand into the seawater-handling business as global offshore exploration booms.

Under the deal, announced by the companies on Tuesday, Ameron shareholders will receive $85 cash per share, a premium of 28% to the stock's Friday close of $66.27. Shares of Ameron climbed 27% in midday New York Stock Exchange trading, while shares of National Oilwell rose 2.2%.

The always-acquisitive National Oilwell, now with $14 billion worth of deals under its belt in just five years, is gearing up for anticipated growth in offshore oil production. Last September, the company paid $500 million for a maker of mooring systems for floating oil production and storage platforms, which it sees as a hot market as drillers move further away from the shore.

"Ameron's marine and offshore products will expand National Oilwell's offering into seawater-handling systems in new oil and gas drilling and (floating production, storage and offloading) vessels," National Oilwell Chief Executive Pete Miller said in a statement.

Activist hedge fund Barington Capital Group L.P. in March waged a hostile proxy battle at Ameron. The fund sought and won a seat on the Ameron board for Barington CEO James Mitarotonda. In filings with the U.S. Securities and Exchange Commission, Ameron called into question Mitarotonda's integrity and qualifications as a director. Barington argued that Ameron was undervalued and that its CEO, James Marlen, had a poor track record leading the company. A representative for Barington was not available for comment on the National Oilwell deal.

National Oilwell said the deal was expected to close in the fourth quarter and should add to its 2012 earnings per share. Ameron makes fiberglass-composite pipe for transporting oil, chemicals and corrosive fluids. The company, which operates in North America, South America, Europe and Asia, provides water transmission lines and fabricated steel products, such as wind towers.